Within each group mapping area (notes and velocities), zones can’t overlap. When you force an overlap by dragging zones one above the other within the same group, the Key Mapping Editor automatically cuts zones in order to make space for other zones. This allows you to add zones or delete mapped areas without having to edit all affected zones directly. You can protect either the selected or unselected zones when dragging zones.
In the Logic Pro Sampler Key Mapping Editor:
Select a zone.
Press and hold Shift-Option to display a horizontal cut icon at the pointer position, then click the zone.
The zone is divided horizontally and a new zone is created. Each zone can be independently edited.
Control Surfaces Support Guide: PDF